Described herein is a method for determining the transfer efficiency of toner in a xerographic print engine. Transfer efficiency is the percent of toner that is transferred from a photoreceptor to a substrate. This information may be used to identify specific types of transfer defects. Upon identification, closed-loop control of the transfer process can be performed taking into account the identified transfer efficiency, to correct or compensate for defects.
Previous post-transfer residual mass sensors have provided information about the average transfer efficiency and could enable limited closed loop control of the transfer system. For example, an Extended Toner Area Coverage (ETAC) sensor may be used to measure residual mass per unit area (RMA) during xerographic setup. The data from the sensor in this case can be used to adjust the transfer setpoints to obtain optimal performance.
The information provided by measuring the RMA with a point sensor like an ETAC is limited to an average measurement of transfer performance. In addition, because a point sensor typically only measures the transfer efficiency at one isolated location in the cross process direction, variations that occur across the belt are not captured by this type of sensor. Therefore, typical ETAC sensors provide only minimal information that is relevant to control of the transfer performance.
Implementations may also use sensors containing arrays of optical sensing elements. In many of these devices, the array of sensing elements provides information across the entire surface of the photoconductor or other substrate of interest. Such optical sensing array devices are termed full-width array (FWA) sensors. These FWA sensors have been used for measuring RMA across all or a majority of the photoreceptor surface. This method allows the residual mass content of the entire image area of the photoreceptor to be captured. However, these implementations typically print predefined test targets, which are issued upon a cycle up or during routine maintenance or setup, and thus do not provide results of transfer efficiency of toner during runtime. During runtime, one cannot print predefined test targets without impacting customer productivity, both in terms of the image production rate and paper waste.